Virulence of entomopathogenic fungi to the Apple maggot Rhagoletis pomonella (Diptera: Tephritidae) and interactions with entomopathogenic nematodes

Authors: USMAN, MUHAMMAD - Ayub Agricultural Research Institute; GULZAR, SEHRISH - Ayub Agricultural Research Institute; WALKLL, WAQAS - Ayub Agricultural Research Institute; WU, SHAOHUI - University Of Georgia; PINERO, JAMIE - University Of Massachusetts; Leskey, Tracy; NIXON, LAURA - US Department Of Agriculture (USDA); Hofman, Camila; TOEWS, MICHAEL - University Of Georgia; Shapiro Ilan, David

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/10/2020
Publication Date: 12/10/2020
Publication URL: https://handle.nal.usda.gov/10113/7256664
Citation: Usman, M., Gulzar, S., Walkll, W., Wu, S., Pinero, J., Leskey, T.C., Nixon, L., Hofman, C.O., Toews, M., Shapiro Ilan, D.I. 2020. Virulence of entomopathogenic fungi to the Apple maggot Rhagoletis pomonella (Diptera: Tephritidae) and interactions with entomopathogenic nematodes. Journal of Economic Entomology. 113, 2627-2633. https://doi.org/10.1093/jee/toaa209.
DOI: https://doi.org/10.1093/jee/toaa209

Interpretive Summary: The apple maggot is a key pest of apples. The insects attack fruit directly. However, a part of the insect’s life-cycle, particularly the pupal stage, occurs in the soil. To control the insect, broad spectrum chemical insecticides are sprayed. Due to regulatory and environmental concerns, research to develop alternative measures to control the pest is warranted. Microbial insecticides such entomopathogenic (insect-killing) nematodes and fungi are environmentally-friendly alternatives to chemical insecticides. In a previous study, we discovered that beneficial entomopathogenic nematodes have potential to kill apple maggot pupae. In the current study, we tested the virulence (killing power) of four species of entomopathogenic fungi. We also investigated combined applications of nematodes plus fungi. Our results indicated that the four species of commercially available entomopathogenic fungi were virulent to apple maggot pupae. These fungi included the following species: Beauveria bassiana (strain GHA), Metarhizium bruneum (strain F52), Isaria javanica (wf GA17), and Isaria fumosorosea (Apopka 97 strain). Additionally, we discovered that combining nematodes with fungi resulted in additive levels of apple maggot mortality. The combination of the fungus, I. javanica, with the nematode, Steinernema riobrave, appears especially promising. In conclusion, our study indicates that both entomopathogenic nematodes and fungi (and their combination) have potential to control apple maggot pupae. The next step will be to test these bio-insecticides under field conditions.

Technical Abstract: The objectives of this study were to quantify the virulence of four commercial available species of entomopathogenic fungi to pupae of Rhagoletis pomonella (Walsh) (Diptera: Tephritidae) and to determine the potential to combine entomopathogenic fungi and entomopathogenic nematodes for biological control of this pest. The four species of entomopathogenic fungi included Beauveria bassiana (strain GHA), Metarhizium bruneum (strain F52), Isaria javanica (wf GA17), and Isaria fumosorosea (Apopka 97 strain). In a small cup experiment, all fungi reduced adult emergence but no difference was observed among the fungal species. Numerically, the lowest adult emergence (50 and 51.7%) was observed with I. javanica and M. brunneum, respectively. Thus, these two fungal species were examined further in a soil pot experiment that also included the entomopathogenic nematodes Steinernema carpocapsae (ALL strain) and S. riobrave (355 strain). These nematode species exhibited high levels of virulence in a previous study. All nematodes and fungi were applied either alone or in combination (fungus + nematode). In the singly applied treatments, no differences were observed between species within the same entomopathogen group (fungi and nematodes). However, treatment with S. riobrave resulted in lower R. pomonella emergence than either fungal species. The combination of S. riobrave and I. javanica resulted in lowest R. pomonella emergence (3%), which was significantly lower than any of the single-applied treatments, yet virulence of the other three combination treatments were not different from their respective nematode treatments applied alone. Additive interactions were detected for all fungus-nematode combinations. The present study revealed that field application of entomopathogenic nematodes and fungi under the tree canopy during summer when the environment is favorable could be an effective option to suppress the R. pomonella population.